Hepatitis C virus is both difficult to treat and a significant cause of morbidity and mortality. It is not understood how hepatitis C establishes infection nor how some patients clear infection. To this end 83 humans exposed to hepatitis C were studied in protocol 00-DK-0221. The immune response (both antibody and T cell) was closely followed and is being characterized. The study is in collaboration with Dr. Rehermann. As an extension of this 28 patients with acute hepatitis C have been followed and treated as indicated. Twenty-five patients (16 women;mean age 43 years) had adequate follow up to be included in an analysis. Symptoms in the acute phase were reported by 80% and jaundice by 40%. Two patients (8%) developed ascites and acute liver failure but both survived. Genotype 1 was most frequent (72%) but many patients (20%) could not be genotyped. Serum aminotransferase levels and HCV RNA levels fluctuated greatly;18% of patients were intermittently negative for HCV RNA. In follow up, 5 patients recovered spontaneously whereas 20 developed chronic hepatitis C or received interferon-based therapy during the acute phase. Among 15 patients treated during the acute phase with peginterferon with or without ribavirin for 24 weeks, all became HCV RNA negative within 4 to 8 weeks, and all except two achieved a sustained virological response with the exceptions being HIV-positive. Side effects (particularly psychiatric) were common and limited the duration of therapy in 30% of patients. To further understand the virological determinants of infection and the development of chronicity, the hepatitis C virus sequence in the early stages of infection is being determined from the same patients. In particular the sequencing effort is focused on the viral sequence before and after treatment, in the two patients who were HIV positive and relapsed. Once chronicity has been established treatment response rates decrease significantly. One of the hallmarks of the hepatitis C virus is its sequence diversity, which is used to classify hepatitis C into different genotypes. Different genotypes have different response rates to treatment. Response rates are typically higher in genotype 2/3. Protocol 03-DK-0136 studies the response of patients with chronic hepatitis C, genotypes 2 or 3, to a decreased dose of pegylated interferon in combination with ribavirin. 30 patients were treated with low-dose peginterferon alfa-2a (90 g/week) and 23 patients with standard doses (180 g/week) for 24 weeks in combination with 800 mg/day of ribavirin. Patients who failed treatment were offered 48 weeks of standard-dose treatment. Viral and serum IP-10 levels were measured and early viral kinetic parameters were calculated. Sustained virological response was achieved in 68% of the low-dose and 84% of the standard-dose treated patients (per-protocol, p=0.81 for non-inferiority). Retreatment was successful in all patients who tolerated full dose and duration. The standard-dose group had a greater first phase decline of the viral levels and faster time to negativity. The second phase slope was not affected by peginterferon dose. Although fatigue and general feeling during treatment were worse for standard dose, hematologic toxicity and depression did not differ between groups. Treatment with a lower dose of peginterferon is associated with some symptomatic benefit but the response is not equivalent to standard dosing. A second study for chronic hepatitis C was performed to assess the mechanism of action of ribavirin in HCV. This was done as protocol 02-DK-0065. Microarray analysis has shown that ribavirin may enhance induction of interferon-stimulated genes (ISGs). The aim was to evaluate early viral kinetics, serum cytokine expression and viral mutagenesis during peginterferon treatment with and without ribavirin. 50 patients with hepatitis C virus (HCV) genotype-1 infection were randomized to receive peginterferon-alfa-2a with or without ribavirin for the 1st month of treatment. All patients then received 48 weeks of combination therapy. First and 2nd phase viral kinetics were evaluated. Serum IP10, MIG and MCP1 levels, representative of ISG response, were measured. Sequencing of part of NS5A and NS5B was performed and mutation rates were calculated. It was found that first phase decline was similar between groups. Patients receiving ribavirin had more rapid 2nd phase kinetics, particularly those with a good 1st phase decline (0.61 vs 0.37 log10 IU/mlmL/week, p=0.026). Induction of serum IP10 at 12 hrs was higher in patients receiving ribavirin than those receiving peginterferon alone (7.6 vs 3.8 fold, p=0.01);however like 2nd phase slope, the difference was more apparent in those with a good 1st phase decline. IP10-induction correlated with 1st and 2nd phase kinetics only in patients who received ribavirin. Sequencing analysis revealed similar mutation rates in both groups. It was concluded that ribavirin improves early viral kinetics, but only in those patients with an initial response to peginterferon. Greater induction of interferon-stimulated cytokines and the correlation with viral kinetics in ribavirin-treated patients, support the notion that ribavirin may act through augmentation of interferon signaling. A second type of chronic hepatitis studied is hepatitis D. Hepatitis D is the most aggressive form of viral hepatitis as well as the most difficult to treat. Interferon therapy is the standard approach. Patients are typically treated for 6 months to a year. Relapse after cessation of therapy is the norm. In protocol 01-DK-0247 patients are treated with peginterferon for 5 years. The dose is titrated to maintain normal ALT and minimize side effects. Patients are evaluated before initiating therapy, and after 1, 3, and 5 years. Patients are excluded if they do not meet protocol-defined criteria for response at the 1 year evaluation. Enrollment was planned for 10 - 20 patients. Thirteen patients have been enrolled, and of the 12 who have had one-year evaluations 10 have met the protocol definition of response. Most of the patients were male (11) and tended to have advanced disease (median baseline Ishak fibrosis - 4). Patients were treated for a mean duration of 144 weeks (range 6 - 300) at an average weekly peginterferon dose of 184 &#956;g. At one year of treatment, inflammatory scores were significantly improved (10.6 2.7 vs. 7 1.9, p<0.01) and this improvement persisted in 4 of 5 patients who had a 3 year biopsy scored. There was no difference in the fibrosis score. ALT decreased significantly after one year (136 143 vs. 46 13, p<0.05) and persistant biochemical response on treatment was achieved by 3 patients (27%). 3/13 patients (27%) lost HBsAg after 24, 37 and 202 weeks of treatment and developed HBs antibodies. Treatment was stopped in these patients at least 24 weeks later;the serological response was durable and was associated with persistent improvement of ALT and platelet count during follow-up. Two patients (15%) died during therapy, one from hepatocellular carcinoma and the other from herpes colitis. Both deaths were not considered related to treatment. There were no other serious adverse events and treatment was well-tolerated overall. 3 patients required a dose reduction due to cytopenias. The primary end point of the study is the evaluation after three years although it is planned to treat patients for 5 years.